This invention relates to a reusable hanger assembly for temporarily supporting a spanner beam during the construction of bridge decks and other elevated concrete slabs.
The forms normally used in construction projects to support the concrete while it hardens include wooden spanner beams and plywood panels. The spanner beams are suspended on hangers between the main structural girders and the plywood panels are installed on top of the spanner beams to provide a flat surface for receiving the concrete. After the concrete has hardened sufficiently to become self-supporting, the forms are disassembled and removed for further use.
The types of hangers currently used to support the spanner beams suffer from various disadvantages, such as structural weakness, high cost, and assembly difficulties. Also, since most existing hangers receive the spanner beam relatively loosely, the assembled forms lack rigidity and are able to shift in position or even collapse when the concrete is poured. Known hangers are further unsatisfactory in that the disassembly and removal of the forms requires considerable time and effort and often results in damage to the forms. More importantly, the disassembly or "wrecking" of the forms involves danger to the workmen because the spanner beams and plywood panels are released together and the entire bulk of the forms must therefore be handled simultaneously.
In one type of prior art hanger, the spanner beam is received in a bracket and supported on a tapered wedge member which is inserted beneath the spanner beam by wedging action. The main disadvantage of this type of hanger is its lack of stability, since the weight of the concrete exerts a force which tends to work the wedge member out of the bracket. As a result, the forms are likely to collapse unless the wedge member is driven in so tightly that its removal is difficult, in which case the time, trouble and danger involved in disassembling the forms is increased substantially.
A further deficiency in the prior art is the lack of a practical maans for varying the haunch of the concrete slab, or its elevation relative to the main structural beams or girders. Existing hanger assemblies typically support the spanner beam at a constant elevation with respect to the girders so that the haunch also remains constant, even though the vertical deflection of the girders varies along their lengths. The concrete slab is therefore not level throughout its length, a result that is particularly undesirable in bridges having a lengthy span because of the large girder deflection near the center of the bridge. Even those hangers that permit haunch variation support the spanner beam only at discrete or stepped levels so that vertical adjustment throughout a continuous range is not achieved.
In view of the foregoing drawbacks associated with existing spanner beam hangers, it is the primary goal of the present invention to provide an improved hanger assembly for supporting the forms used in the construction of elevated concrete slabs such as bridge decks and the like.
More specifically, it is an object of the invention to provide a hanger assembly which supports a spanner beam in a rigid position between a pair of spaced girders. It is an important feature of the invention that each end of the spanner beam is tightly retained in the hanger assembly such that the hangers, spanner beams, and girders form a rigid structure in the assembled condition.
In conjunction with the preceding object, it is a further object of the invention to provide a hanger assembly of the character described that supports the spanner beam with increased stability and resists any tendency of the spanner beam to release when the concrete is poured.
Another object of the invention is to provide a hanger assembly of the character described which permits the assembly and disassembly of the forms to be carried out quickly, easily and safely.
Yet another object of the invention is to provide a hanger assembly of the character described that includes adjustable means for varying the haunch of the concrete slab throughout a continuous range.
A further object of the invention is to provide a hanger assembly of the character described that is economically manufactured and yet constructed ruggedly for repeated use.